NNR Plenum exposed after >5 years

[Tanzy]

Today, I was removing sand from my tank and finally dug deep below 4" of sand to reach the plenum. The top 2" of sand was filled with muck and the water was muddy green. Totally opaque! Below that, nearing the plenum, the water became crystal clear. Apparently, fine sediments never got deeper than 3" into a sand bed. The plenum space is still there and contains no fine, greyish brown sediment that was found in the top layer of sand. It has a fine layer of sand that got through the netting at the bottom, that's all. The green fibreglass netting is not broken and remains slightly elastic. The single layer of green netting is capable of retaining almost all the #1 sand with only negligible amount getting through. No hydrogen sulphide smell was encountered.

Photos later.

[Mellow]

Interesting! I'll keep you guys updated about what I can find once I unearth my plenuum too..In the midst of tearing down my tank....

[Navyblue]

Nice testimony definitely will help those deciding DSB or plenum.

Too bad I don't use a plenum...

[FuEl]

Interesting! I'll keep you guys updated about what I can find once I unearth my plenuum too..In the midst of tearing down my tank....

Mellow..if you have not done so it would be informative for fellow reefers if you could use a syringe to test the water below the plenum and see if there is any difference between that and the main water above the sand bed. I have this feeling that phosphates and maybe even nitrate levels might be higher below.. Read it before in an article that plenums might actually be nutrient sinks.

[tineng]

help a bro clear his tank before...very matured tank, the moment the plenum was removed, whole room stink like hell....but regard didn't had time to meaure the water quality....

Mellow, if you clear your tank, why not do a test on the 2 water to let us know????

anyway, will be setting my a tank soon....but still stuck in deciding if DSB or plenum better.....

[Mellow]

Just cleared my tank and removed the plenum yesterday. Didn't test the water coz I don't have the necessary test kits. But my observation is very similar to Tanzy.

Really dirty on the top layer of the sand. But as I got to the plenum area, water is clear and free from all the detritus buildup etc. I'm not sure how hydrogen sulphide smells like, so haven't got any idea if they were present though.

And lastly, about 2cm down from the top layer of my sand bed, the sand were all clumped up into huge chunks of sand stone. Had to use a screwdriver to break them apart before I could even get to the plenum space. Any thoughts or things to add regarding this phenomena? What I know is that certain chemicals causes the precipitation and binding of the sand together. Is it correct?